33047ffddc
* Update ReentrancyGuard for Istanbul Hard Fork
Changes:
Added L37, `_guardCounter = 1;`
Rationale:
The planned _Istanbul Hard Fork_ will implement [EIP 2200](e4d4ea348e/EIPS/eip-2200.md), which implements "net gas metering" for `sstore` operations. If the final value of `_guardCounter` is unchanged relative to the original value of it, a gas refund will be applied and charges for changing the value of `_guardCounter` will effectively not exist. This ends up being cheaper than the current implementation ONLY AFTER Istanbul. Before Istanbul, the added line actually ends up costing more gas.
Note that if `_guardCounter` is `0` initially, the initial cost and subsequent refund will both be larger than if `_guardCounter` is `1` initially. Although in both cases, the net gas cost (`gasCost - gasRefund`) are equal, it's better in terms of cost to have both the gas cost and refund smaller, as there is some limit to the percentage of a gas refund that can actually be realized.
* Update CHANGELOG.md
Added note for change to ReentrancyGuard.sol
* Update ReentrancyGuard.sol
* Update CHANGELOG.md
OpenZeppelin Contracts is a library for secure smart contract development. It provides implementations of standards like ERC20 and ERC721 which you can deploy as-is or extend to suit your needs, as well as Solidity components to build custom contracts and more complex decentralized systems.
Install
npm install @openzeppelin/contracts
OpenZeppelin Contracts features a stable API, which means your contracts won't break unexpectedly when upgrading to a newer minor version. You can read ṫhe details in our API Stability document.
Usage
To write your custom contracts, import ours and extend them through inheritance.
pragma solidity ^0.5.0;
import "@openzeppelin/contracts/token/ERC721/ERC721Full.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721Mintable.sol";
contract MyNFT is ERC721Full, ERC721Mintable {
constructor() ERC721Full("MyNFT", "MNFT") public {
}
}
You need an ethereum development framework for the above import statements to work! Check out these guides for Truffle, Embark or Buidler.
On our site you will find a few guides to learn about the different parts of OpenZeppelin, as well as documentation for the API. Keep in mind that the API docs are work in progress, and don’t hesitate to ask questions in our forum.
Security
This project is maintained by OpenZeppelin, and developed following our high standards for code quality and security. OpenZeppelin is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
The latest audit was done on October 2018 on version 2.0.0.
Please report any security issues you find to security@openzeppelin.org.
Contribute
OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the contribution guide!
License
OpenZeppelin is released under the MIT License.